Twisted wire brushes for application of liquid-type cosmetics, such as for application of mascara to the eyelashes, are well known in the art. The brushes are designed to pick up and hold a supply of mascara from the cosmetic container, and then deliver the mascara to the eyelashes as the brush is combed through the lashes by the user.
Twisted wire brushes conventionally are manufactured by disposing a plurality of individual lengths of bristles transverse to and between substantially parallel, slightly spaced-apart thin metal wire lengths, such that the wire lengths generally bisect the filament lengths at their midpoints. Most typically, the parallel wire lengths comprise the two substantially equal leg lengths formed from bending a single length of wire into a U-shaped configuration. The wire lengths are then twisted together to form a helical core, causing the bristles disposed between the wires to be clamped therebetween at about their midpoints. In the twisting and clamping, the segments of the bristles on either side of the clamped midpoint are caused to flare radially outward from the core and so form an elongate bristle brush portion of generally circular cross-section. The brush is generally provided with a handle which can comprise, or be affixed to, a cap or other closure for the cosmetic container. The bristles are usually comprised of nylon filaments.
It is known in the art that this helical wire twisting method for forming cosmetic applicator brushes typically leads to a brush configuration in which the bristles tend generally to follow the helical pattern of the twisted wire core, i.e., whereby the tips of the bristles define a helix. Standard mascara brush designs of the 1960s and 1970s used smaller diameter bristles in fairly large numbers of bristles per turn. The state of the art then evolved to a somewhat larger diameter bristle, as defined in U.S. Pat. No. 4,887,622 entitled “Brush for the Application of Mascara to the Eyelashes.” The patent discloses a mascara brush having a reduced number of bristles, said to be 35% to 80% less than in conventional mascara brushes, ostensibly of larger diameter, than the bristles employed in conventional mascara brushes at the time. This was believed to provide a better application of mascara and separation of lashes. The patent specifies mascara brushes having a bristle diameter from about 0.10 to 0.25 mm (e.g. about 0.004 to 0.010 inch) (4 mil to 10 mil) and with from approximately 10 to 40 bristles per turn of the helix. The concept of a mascara brush having larger diameter fibers was further discussed in a recent PCT application no. PCT/U.S.01/04555. This application is directed towards mascara brushes made from filaments that are relatively large but soft. Specifically, the application describes mascara brushes having preferably having 7–14 bristles per turn. The bristle filaments are defined as preferably being from 0.010 inch to 0.013 inch (10 mil to 13 mil). Most critically, the bristles are defined as being relatively soft being made of a thermoplastic elastomer having a durometer of between 62 Shore D and 82 Shore D, but most preferably about 72 Shore D. PCT application PCT/US01/04555 essentially defines a mascara brush made with a duPont Filaments filament sold under the trademark “Supersoft.” The “Supersoft” filaments have a durometer of 72 Shore D and are available as solid filaments or as triocular filaments having three hollow voids.
Mascara, which is typically highly viscous, tends to clump when applied to eyelashes. The clumps of mascara are typically combed out as a finishing step to the application process. Stiffer bristles are thought to be better suited for combing out clumps and properly separating lashes. However, the combing and separating functions are thought to be better accomplished with brushes a having relatively open bristle envelope or brush surface, i.e., an envelope or surface that has numerous or wide clearances or spaces between bristles to make the brushes more ‘comb-like’. This function is not well served by traditional mascara brush designs having smaller diameter bristles with higher bristle density. A mascara brush with softer, more numerous bristles has been generally thought to be well suited for applying mascara but less well suited for combing out clumps and separating lashes. Conversely, a brush with stiffer, fewer bristles has been thought to be well suited for combing and separating lashes but less well suited for applying mascara to lashes. While a separate brush can be used for each function, i.e., a soft brush for application and a stiff brush for combing, a single brush that can both apply mascara and comb out clumps would be preferred for the convenience of the user. An example of a brush said to provide good application and combing characteristics is shown in U.S. Pat. No. 5,238,011 to Gueret. The Gueret patent discloses bristles made of a soft material having a shore hardness of 20 A to 40 D (as noted above, a conventional bristle typically has a durometer of over 85 D), and a large diameter in a range of 0.004 inch to 0.014 inch (4 to 14 mil) (0.10 to 0.35 millimeter). As disclosed by Gueret, the diameter is said to be sufficiently large to prevent too high a degree of suppleness. The resulting brush is said to have the same degree of suppleness or softness as a conventional softer brush.
Nevertheless, there can be a perception of bristle hardness to the mascara user. In many prior art brushes, the prior art approaches have not provided a brush with a combination of all the desirable features for a mascara brush—a soft bristle feel, combined with bristle stiffness suitable for high viscosity mascaras, while still providing both a good combing effect as well as high mascara loading.